The advent of optical communication links has offered increased data communication capabilities over their lower frequency electromagnetic radiation counterparts. This increased capability has not come without increased costs, and there is a great need for low cost data links in the optical frequency band. While component expenses are often the source of the high costs of data links, another is the labor input to the alignment of the devices in the links. To this end, there is a great need to effect a data link that is not plagued by the need of labor intensive alignment efforts in the manufacture of the data links.
Bi-directional data links are generally composed of an optical transmitter such as a laser or LED that transmits modulated light signals at a first frequency and a photodetector such as a PIN photodiode that detects a light signal at a second frequency different than the transmission frequency, thereby reducing or eliminating the possibility of signal cross-talk. The light of the transmitted and received frequencies is conveyed via a common optical fiber, and can be sequentially or simultaneously transmitted or received. The module having the transmitter, receiver and optical coupling elements is located at one end of a fiber link. An example of such a bidirectional optical module is as shown in U.S. Pat. No. 5,127,075 to Althaus, et al., the disclosure of which is specifically incorporated herein by reference. Althaus, et al. discloses a bidirectional link that uses a hermetically sealed TO can transmitter and a hermetically sealed TO can receiver that are mounted in a common hollow housing to effect the bidirectional module. The TO cans are mounted in an orthogonal fashion and an optical fiber transmits light to and from the module. A beamsplitter is located in the optical path of the fiber and directs light from the fiber to the detector. This beamsplitter can be wavelength dependant or a proportional splitter that deflects light in a defined intensity to the detector and the receiver. The wavelength selectivity requirement of the detector and emitter is then effected by selective wavelength filtering prior to the light's impinging on the detector or emitter. The various subassemblies are then adjusted for optical alignment and finally fixed in final position. The drawback to this configuration is that the autonomous emitter and detector are aligned in the common housing either iteratively or successively with the various optical elements of the system to optimize the input and output performance. This approach is clearly a complicated and labor intensive approach, which accordingly increases the cost of the device. Furthermore, in the preferred embodiment, the lens element for the light emitter is within the encapsulation, and the optical alignment of this due to the close proximity of the lens to the emitter is rather difficult, and thus a labor intensive effort that serves to further increase the cost of manufacture.
Another example of a bidirectional link is as disclosed in U.S. Pat. No. 5,347,605 to Isaksson the disclosure of which is specifically incorporated herein by reference. This reference like the Althaus, et al. reference discussed above also makes use of an orthogonally oriented emitter and detector assembly having the emitter and detector mounted in a housing. The alignment of the emitter and detector is effected by the use of a rotatable member that allows relative positioning of the emitter, detector and optical focusing elements. While the rotating member facilitates the alignment process, this reference like the Althaus reference requires active alignment of the emitter relative to the detector, an alignment process that is complex, labor intensive and thereby drives the cost of the device. What is needed is a bidirectional link that has the advantages of hermeticity and low cross-talk signal transmission and reception, and yet is fabricated with great simplicity and thereby low cost.